: Oxidative stress is thought to participate in vascular dysfunction and remodeling that accompanies angiotensin II (AII)-induced hypertension, but the source and cellular sources of oxidant species and their precise role is poorly understood. Recent studies in the laboratories of the two PI's have elucidated a novel role for the aortic adventitia as the site of elaboration of both superoxide anion (O2-) and nitric oxide (NO) radicals, indicating that the adventitia is a major site of oxidative stress. New studies indicate that the increased elaboration of O2- by AII is indicated by prominent nitrotyrosine staining of the adventitia, likely as a result of production of the reaction product of O2- and NO, peroxynitrite (OONO-). There are many sources of O2- in the vascular wall, but recent studies indicate that multiple subunits of the neutrophil NAD(P)H oxidase are present in the adventitia where O2- is greatest. Preliminary studies in which AII was infused into mice that are deficient in one NADPH oxidase subunit, gp91phox, show a blunted aortic O2-, hypertrophic, and proliferative response to AII compared with wild type mice, despite a similar hypertensive response. Proposed studies in rats and mice will elucidate the hypothesis that oxidative stress mediated by adventitial NAD(P)H oxidase-derived O2- participates in the myogenic, hypertrophic, and proliferative vascular response in AII-induced hypertension. The proposed studies will also take advantage of preliminary work on Apo E deficient mice (EKO) to determine the significance of AII-induced oxidative stress in atherosclerosis. Preliminary studies in these mice indicate that captopril and losartan reduce atherosclerosis (suggesting a role for AII), and that hypothetically under the influence of AII, there is increased production of O2- and OONO-, as indicated in preliminary studies by nitrotyrosine. Studies in Apo E deficient mice that overexpress human Cu/Zu SOD and double knockouts deficient in Apo E and gp91 phox or the AII type receptor, will help to elucidate the hypothesis that AII-induced oxidative stress contributes significantly to vascular dysfunction and remodeling in atherosclerosis.